Placement of lead extensions in a patient may be required in a number of situations, such as placement of a medical device where the lead extension electrically connects an implantable electrical medical device to an electrical lead.
The use of lead extensions can serve multiple purposes. For example, lead extensions can electrically bridge the distance between a suitable implant site for an implantable pulse generator (IPG) and a lead implanted at tissue targeted for stimulation or sensing, where the lead alone may not be long enough. In some cases, an IPG may be implanted in the chest and a lead may be specifically configured to be implanted in the brain and accordingly the lead may be particularly thin and have external material suited for contacting brain matter. These design considerations may render the lead unsuitable for bridging a connection through the neck, as a lead that spans the neck may need to be durable, robust, extendable, and flexible enough to survive the everyday rotations, articulations, and extensions of the neck. In some cases, the lead extension may be specially configured to handle the neck environment (e.g., by being thicker and more flexible) while the lead may be specifically configured to handle the brain environment (e.g., thin enough to minimize interference with brain tissue and rigid enough to maintain implant position and orientation).
Implantation of lead extensions bridging the head and chest may be complicated by the lead extensions tangling when pulled though a subcutaneous tunnel between the head and chest. Tangling of the lead extension can increase the chances of the extension catching on something and/or requiring an increased pull force and/or a remedial surgical technique.
Sometimes carrier units are used to temporarily house a distal end connector of the lead extension to secure the lead extension to the tunneler and allow the tunneler to pull the lead extension through the subcutaneous tunnel. However, the carrier element in these cases wraps around distal end connector, which can make for a larger profile of the assembly as it is pulled through the subcutaneous tunnel, increasing resistance within the tunnel.
In some patients, resistance can be experienced while removing the tunneling device with the lead extension. Excessive force to remove the tunneling device with the lead extension can result in carrier failure.